solid rear differential

[AndyR]

I was just wondering what everyone thought about running a solid/ spool type rear differential. I know there are a lot of good things about it like weight savings, simplicity, and consistent handling.
How do you think these advantages compare with possible handling advantages you get by using a zexel or something like that.
I realize that with a solid rear diff, the car will tend to push more, do you think that setting up the suspension correctly would make this a small issue?

[AndyR]

I was just wondering what everyone thought about running a solid/ spool type rear differential. I know there are a lot of good things about it like weight savings, simplicity, and consistent handling.
How do you think these advantages compare with possible handling advantages you get by using a zexel or something like that.
I realize that with a solid rear diff, the car will tend to push more, do you think that setting up the suspension correctly would make this a small issue?

[rjwoods77]

Formula 500 doesnt use them and they fly. Different car but still. If you design you rear suspension to allow for passive steering effect and use a locked rear you shouldnt have much of a problem. Just look at the benefit. All that juicy weight and space you save. Also it isnt uncommon for leakage on those things. Even RIT got screwed by a diff leak one year. Get rid of it. Tune any bad behavior out.

[Frank]

i see locked rear like this.....

it's effects are "amplified"

for instance, the amount of rear brake bias has a greater determination upon corner entry understeer / oversteer; than does an open/limited slip rear

and similar with acceleration (with traction control makes it work very predictably)

simply saying a spool makes you understeer (insert similar inexperienced bullshit comments) is simply not true

this wheel in the air stuff isn't really true either... man, we're nearly all running very narrow track cars, the inside tires are not carrying much weight

and btw, narrow track spool cars aren't hard to push in the pits anyhow; just lean on the roll hoop to unload the inside tire


Frank

[MikeWaggoner at UW]

"narrow track spool cars aren't hard to push in the pits anyhow; just lean on the roll hoop to unload the inside tire"

Won't that require a second push bar? http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

[Patrick W. Crane]

Look at it like this. If your two rear tires are locked together at the same speed of rotation, then when you turn a corner they are going to fight each other for grip (the turning circle of the inside wheel will have a smaller radius, and doesn't want to turn as fast as the outside wheel). Since the inside tire is mostly unweighted, it will lose and spin the same speed as the outside wheel.

The point is, when turning a corner with a solid rear end, you inside rite will slip, and you will only have the benifit of kinetic friction for that tire helping you in the coner (dick all).

So it's a choice of simplicity versus fuctionality. How much speed do you gain on the straights due to lighter weight? How much cornering grip do you loose in the corner due to sipmlicity?

I reallise there is more to it than that, but that's a good chunk of it. Design in a limited slip - test it - switch in a solid - test it. justify you choice.